Electron discharge apparatus



4 ,ASheets-Sheet l G. K. TEM` ELECTRON DISCHARGE APPARATUS Filed May 4, 1938 June 17, 1941.

rJune 17, 1941. G. K. TEM. 2,245,624

ELECTRON DISCHARGE APPARATUS Filed May 4, 1938 4 Sheets-Sheet 2 1 F/G. 6 g .exrNs/ou @NPR/mer 4 cArHooE Sa F/G cz sEcoNoAkr VOL 7'$ PER STAGE /Nl/ENTOR G. K. TEAL .9V

A 7' TORNEI June 17, 1941.

G. K. TEAL A 2,245,624

ELECTRON DISCHARGE APPARATUS Filed May 4, 1938 4 Sheets-Sheet 4 F/G F/G. /2

/N VEN TOR Mam 6M A T TORNEV Patented June 17, 1941 ELECTRON prscHAnGE APPARATUS Y ordonKQTealQNew York, N. Y., assignorto Bell Telephone Laboratories, Incorporated,A New V York,A AN.V Y., a corporation of New York y f f AppxiationMayi, 193s, serial No.A 205,931.

. This invention' relates to electron discharge apparatus vand more particularly to" vkelectron discharge devices having one ofr more secondary electronv emitting 'electrodes` andV commonly known as electron multipliers; f Electron vmultipliers 'of Ya' typ-e Acomprehended by this invention comprise a sourcey of 3 primaryy electrons, such as a photo-.electric.-cathodeg Aan anode or collector electrode spaced from? the 'pri-H mary source, andone or a 'plurality of secondary electron emissive cathodes4 between the source' and the anode-or Vcollectorelectrode; Primary electrons emanating from -'the source ae` drawn to and impinge. upon the secondary cathode' nearlf est thereto and result infthge emissinfof Asecond-" ary electrons therefrom. Because of lthe characf ter of the secondary 'cathodeyamong other fac? tors, the secondary currenty emanating therefromis greater than the impinging primarycurrnt so that in effectV an 'electron' multiplication or' amplification is obtained. The seconfdary` 'current is drawn to the anodey or' collector electrode', or to the next succeeding secondary' cathode a i plurality of such cathodesare employedl" u The efficiency and other characteristics'of such an electron 'multiplier are deper'iden't to a largey extentr upon the fields extant between the succes` sive electrodes, and partitura-fly adjacent the' emissive surfaces of the various cathod'es; and

upon the degree of concentration of the ele t t @from streams between successive electrodes'.

One broadand generallobj'ect' of the invention l is to improve the efficency'and operating char-f acteristics of electron multipliers.'

More specifically, objects of this invention are:

'ro obtain a menue-'grae of' cenverg'ence 'or the electron streams between successive":'elecj-J trodesin electron multipliers; f

`To Iobtain relatively sharp focussing'y of Athe," electronsl emanating from each of Vthe cathodesi, upon restrictedv portions Vof thevfneoxt' succeeding electrode;v M w To assure strong elds awayfrom the emissive surfaces of the cathodes' whereby copious er'nission of electrons and voltage, saturation maybe achieve-d; n To enable voltage s To avoid the fv rm 7tion o secondary electrons;

aturati'on Vorf -the secondary electron current `or currents at relatively low'lpbf e tential differences between successive electrodes; Y,

To decrease the transit tim'eof electrons*be-Y t f Spewh'r'g in' fha] vicinity of the emissive surfaces ofthe c'athodes';

To reduce the effectsof initial velocity of the YTo enable control of thetrajectories of the electrons owing to the secondary cathode or cathodes whereby the incidence of such electrons, most conducive to copiousA emission of secondary 5 electrons may be obtained; and Y v .To facilitate control of the gain of an electron multiplier and modulation of the output current thereorf.-V l Y In vone illustrative embodiment of this invenlggti'on, an electron multiplier Vcomprises a primary photoelectric cathode, a collector electrode spaced from the primary. cathode, and a plurality of secondary cathodes mounted in staggered relation in two rows, between. the .primary cathode .and the collector electrode or.4 anode. The secondary cathodeshave their opposingY surfaces electron emissive and preferably are of such form and are so disposedthat in the aggregate they have glide planesymmetry. i. v

,In accordance with `one feature of this invention, thesecondary cathodes have their opposed surfaces` generally concave so ,that an electron lens effect is obtained and focussing of the elec,- trons emanating from leach of the cathodes is Zfeffetedt Y l Y y In accordance with another feature of this invention one orJnore auxiliary electrodes are provided between the rows of secondary cathodes for producing ,strong fields in such relation to the 'llemissive surfacesfthat high acceleration of the emanating electrons and a high degree of convergence ofthe various, electron streams' are obl ample, sm'allarea linear'rods or wiresjeach of Snwhich may beparallel and substantially centrally located with respect`to"a `corresponding one of the secondary electron emissive surfaces'.

The invention and the foregoing and other features V thereof will be understood' more clearly and 49 1ifully from the following ydetailed description with referenceVA to the accompanying drawings, in whicll:`

1"is a perspective View of any electron multiplier illustrative of one "embodiment of this inlavention'g a portion ofthe 'enclosing vessel being broken away to showthe electrode assembly more cl'e'arl'y;

2 is a side View, partly in' section, of the electrode assembly of the electron multiplier illus- Qtrated iniigi;

TFigli' is an enlarged perspective view'of one of the' secondary c'athdes of the electron multiplier illustrated lin Fig: 1;'

`Fig. 4 is a diagrammatic side View of the elecf5trodes in the'.` electron multipli-erV shown i-n Fig. 1,

tained. "The auxiliary electrodesinay be, for ex-` illustrating the form and space relation thereof;

Fig. 5 is a circuit diagram showing one manner in which the electron multiplier of Fig. 1 may be operated;

Fig. 6 is a graph illustrating a typical operating characteristic of the multiplier of Fig. 1, operated as illustrated in Fig. 5;

Fig. 7 is a graph showing a family of lines indicative of the operating characteristics of the multiplier of Fig. 1 with various interelectrode potentials;

Figs. 8, 9 and 10 are diagrammatic side views to scale showing modifications of Ythe embodiment illustrated in Fig. 1; f

Fig. 11 is a perspective view of an electron multiplier illustrative of another embodiment of this invention, portions of the enclosing vessel and of the electrode structure being broken away;

Fig. 12 is a side view, mainly in section, of the electrode assembly in the `multiplier illustrated in Fig. 11; Y

Fig. 13 is a top View along line |3| 3 of Fig. 11 and partly in section, of this multiplier;

Fig. 14 is an enlarged perspective view of one of the secondary cathodes included in the structure shown in Fig. 11;

Fig. l5 is a circuit diagram illustrating one manner of operating the electron multiplier shown in Fig. 11;,and

Fig. 16 `is an enlarged diagrammatic view indicating the electron trajectories in the electron multiplier shown in Fig. 11. Y

Referring now to VVthe drawings, the electron multiplier illustrated in Figs. 1-to 4, comprises a highly evacuated vitreous enclosing vessel .20 having an inwardly extending stem 2| at one end provided with an intermediate annular flange.r

, The-secondary cathodes are arranged in staggered relation in two parallel rows, are substantially identical in form and construction and preferably are spaced-so that in thev aggregate they have glide plane symmetry. That is vto say,-r

these cathodes are of such form and are 1so disposed that if one row were displaced a distance (Fig. 4) parallel to the medial plane between the two rows. (as A-A in Fig. 4), each of the secondary cathodes in the one row would be exl secondary is of material import inasmuch as it enables the A attainment of strong elds away from large portions of Aeach of the secondary cathodes whereby copious emission and convergence of the electron streams may be attained expeditiously.

As indicated in Fig. 4, the secondary cathodes in each row are equally spaced from each other and from the medial plane between the two rows.

As shown clearly in Fig. 3, each of the secondary cathodes 21 comprises a backing member or plate 29, preferably of sheet metalsuch as nickel, having opposite edge flanges 30, 'and a formed sheet metal member having end portions 32A affixed to the flanges 30, as by bent wire fasteners or rivets 3|. The formed metal member includes also a concave or dished portion 32, the concave. surface of which is treated or coated to renderit capable of eiiicient and copious emission of secondary electrons. For example, the formed member may be of sheet silver, the concave surface of the portion 32 being treated to form a matrix or coating including silver, caesium oxide and some free caesium.

As will be noted from Figs. `2 and 3, the concave surface 32 of'each secondary cathode comprises a central or intermediate portion and end baffle or barrier portions, the latter extending at unequal angles from the intermediate portion and toward the medial plane between the two rows. These end portionsv and also the end members 32A extend between the'intermediate parts of the concave surfaces of adjacent or 'succeeding electrodes in the :same rowl and thereby prevent one secondary electrode from producing a field component near thenext adjacent cathode which might tend to retard the electrons emanating from suchnext :adjacent cathode. The upperend portions ofeach secondary cathode, and particularly the upper end members 32A, in addition serveto create astrong accelerating eld at the'lower portion'of the next adjacent cathodein'the 'same row, i. e., the second `preceding cathode, and also at substantially the entire surface of the next preceding cathode. Furthermore, the end members 32A aid in providing a closed, substantially completely lshielded electrode structure;

Preferably, the dished orconcave portion v32 of each` of the secondary cathodes is'provi'ded with side flanges 33, which may be integral therewith, to prevent lateral dispersion of the electrons emanating from the coated or treatedsurfaces f If desired, the cathodes I21 may be dished or curved somewhat between the side iianges 33 and toward the backing plate29 to further prevent lateral dispersion of electrons emanating from the surfaces 32; v f

Each of the secondary cathodes 21 is supported from two 'of the cross-wires .24 by a pair of metallic U-shaped wires or brackets 34 aixed to the backing memberA or plate 29. Electrical connection to these cathodes may be established through leading in conductors 35 sealed radially in the flange 22 and extending outwardly through the stem.2|.

The` primary cathodeY 25 may be substantially identical in construction to the secondary cathodes 21 with the addition of a metallic overhanging portion or projecting plate-element 36 afiixed to one ofthe end portions 32A by wires or rivets 31. The overhanging portion 36, being electrically integral With the cathode, provides field components assisting in focussing the electrons emanating from the concave surface of the dished portion V32' of the primary cathode so that these electrons impinge upon desired. portions of the rst secondary cathode 21. This concavesurface or screen electrode 28 `may @be lmaintained .at .a

is photo,electrically*active.-.V For ,example, it may befa coating or {matrix/t including silterolcaesium oxideandifree caesium. v

If the,-cathode;25 is to benergizedotherithan 'by :light :focussed thereon, -the' i concave or t-emissive. surface "thereoffmay -fbe treatedgor coatedin other Ways. Flor-"exampleif it istorbe'fenergized by van' velectron A:str-cam, 1producedbyfan'electron thermionic cathode or ,f otherwise, `the :concave @surface of ithe :primary'icathode may fbe coated or treated to have thereon a secondary electron emissive surface. The active vmaterial may be, :for-example, nickel, :aluminum 'or vany oxidized material exhibiting ;a=high work function.

Thezprimary cathode 25, similarly to the ysecondary cathodes, maybe vsupported from two'l of the cross-members 24 by two vU-shapedlbrackets 34 to oneof which a leading-in conductor 38 is connected. YAs illustrated in Fig. 4,.the primary cathode is setback somewhat, as compared with the secondary 'cathodes' in line therewith,1to allow energization, as by a beam of light,vof substantially all of the photoelectrically'active surface thereof. y' u' Thelco'llector electrode or anode `26`-comprises a metallic baseplate 39 supportedffrom one ofthe cross-wires '24 by a pailrof 4rigid rods or lWires 40, and a metallicfplateffM, affixed I`to the base plate 39 as by weldingiand extending at an acute angle thereto and toward the secondary cathode 211. 'Electrical connection tothe anodeor col-- lector electrode may be established through a leading-inconductor (not shown) sealed in lthe side wall of the vessel 2|) to reduce leakage and capacitance to ground.

The shield or screen electrode 28 vis supported by wires 42, only one 'of which is showin, and comprises two metallicy plates 43 and 44, one (43) of which is substantiallyparallel tothellow'er en d portion of thesecondary cathode 2119 and co planar with the baseplate ,ofthe anode or col-- lector electrode and the other 4(44) of =which extendsbetween thesecondary cathode219 andthe anode or collector electrode. The shield onscreen electrode 28 includes also a reticulatedor grid portion 45 Aextending diagonally between the plates43 and44 and affixed-thereto. This Aelectrode 28 serves rtosheldrthe cathodesl'iieand f2'l10 from the anodeorcollector electrode ,26.50 that voltage iiuctuations uponfthe flatter donot-:deleteriously affect the fields .adjacent-these secondary cathodes, .and also to assure flovw of substantially allthe I secondary electrons emanatingfrom the cathode A219 to the cathode 211. ,Electrical connection to .the electrode 28 may beestablished through a leading-in conductor, not shown,

sealed inthe fia-nge 2v2. I l

During operationofthe electron multiplier, as shown in Fig. 5, the secondarycathodes are maintained at successively eqi1allyhigherpositive potentials with resect to the next preceding cathode.`

For example, the first secondary cathode 2li-may be-maintained at a positive-potential'oftheorder of 25 to 100 volts with respect to the 4:primary cathode, the next secondary cathode212may be maintained of the order of 25zto-f100 volts p'osi# tive .Withrespect t-o the cathoder2'l1 and each succeeding secondary cathode may 'be'maintained of the Aorder of 25 to -100 volts positive with respect to the next preceding one. "Ihe desiredpotentials may be obtained from a potentiometer arrangement including a resistance '45 in shunt with a source41, such as a rectifier, The shield similarvoltzage, e. g. ,25 to 10,0 .voltsgpositivewith respect totthe secondary cathode-2110, asv-by-a battery w48; and the anode 226 likewise ;rnaintain d 4of theforder of"25;to 100 voltspositive with respect to the shield or screen electrode 28as. by a battery 49. An output or utilization circuit Vmay be connected between the cathode 211"` 'and the anode or collector lelectrode 26 through the batteriesn and 4 9 asshown in Fig. 5.

When theprimarycathode 25 is energized, as by a beam of light, corresponding to a signal to be translated, emanating from a source of'variable; light,` photo or primary electrons are emitted fromzthe activated concave surface 232 of this cathode. Under the influence of the higher-potential upon the secondary cathode 211, andthe fields extant between the cathodes 25,1211, 2-12- and 213 the primary electrons flow to andnimpinge uponfthe activated concave'- surface of the secondary cathode 12'111and cause vthe emission of seconda'ryelectrons therefrom. f Because -of "the treatment or coating of the concave V'surface of the secondary cathode, as described rffheretofore, the secondary electron current ,Willbeggreater, for examplefftto times greater, thanthe impinging primary electron current. I-IencafinA effect, an electron multiplication and, ,therefore,jamplica' tion. of the signal, corresponding totheflightibeam will result. i v

,The secondary .electrons `emanating from vthe cathode `2711 willbe drawn toward rand irnpnge upon the concave surface of the cathode :212,and causethe `emission of a still 'greater number of secondary electrons with a correspondinggfurther amplification of the signal being translated. 'This phenomenon of electron ,multiplication and .amplication isrepeateda eachvofthe succeeding secondary cathodes .213 to 2,110 inclusive. The electronsemanating `from the last cathode i211 flow to theanodepr collector electrode l Zlarid constitute'the output current of the multiplier.

The paths traversed by the, several ,electron streams .are indicated generally by the arrows between electrodes in Fig..5. v. y y

One .of the principal factors determinative of high efficiency and lstable -andsatisfactolybperating v.characteristics of `electron multipliers of the ltype comprehended by Vthis invention and exemplified by thedevice illustrated in-Fig. 1 is the degree .of convergence of the severalelectron streams emanating from the `variousL cathodes. It is necessary forY the attainment ofhigh efficiency and satisfactory vcharacteristics .that substantially all of the secondary electrons ern- -anatinggfromieach secondary cathode `loe drawn away therefromY and caused to impinge upon the next succeeding electrode. Preferably the irn- .p'ingernentshould occur over arestricted areaof theyemissive surface of .the receiving electrode.v

In accordancev with one ,feature of this .jinvention, the Various cathodes are so shaped .and disposed that Vavpstrong'i-leld away from ya large portion of the emissive surface of each cathode obtains Yso that Asulistantially all of` the emitted electrons are accelerated away from .this surface; 'I he shaping 4and space relation a-re such,"`fur thermora'thatthe electrons emitted from ea-'ch surface are focussed upon ay restrictedportion of the -emissivesurface Vofjthe next succeeding electrcde.` y

Generally, as noted heretofore, the V*en'cissive surfaces of the secondary cathodes vare concave. 'Ihel -degree #of convergence Vof y ther electron Y streams 4andtheintensty `and direction of 'the fields in the vicinity thereof have been found to be fairly critically dependent upon the relative parameters of these surfaces. Specific relative parameters for one embodiment of this invention expressed in units are indicated in Fig. 4, wherein 11:11.62 o :0.78 12:10.78 :c :6.20 c: 2.90 r1g4-20 d: 0.84 r24-43 m: 1.63 r3 r1, r2, and r4 n: 4.5.3 r4g0-23 and :75 degrees;

The values given for r1, r2 and r4- it may be noted, are Ybut approximate inasmuch as the curves indicated thereby are not continuous single circular arcs.

In a specific and illustrative embodiment, the unit may be 0.0666 inch.

As tothe collector or anode 26 and the shield or screen electrode 28, the parameters indicated in Fig. 4 and expressed in units, Aa specic unit being 0.0666 inch, may be and` p:51.2 degrees and 13:17 degrees.

The grid .portion 45, it will be noted, subtends the angle bounded by the members 39 and 4| of the anode or collector electrode.

As indicated in Fig. 4, with respect to the primary cathode, f may Ibe 5.625 units, g may be 2.51 units :and p may be 115 degrees, a unit in a specific embodiment --being 0.0666 inch, as noted above.

In an electron multiplier of the construction illustrated in Fig. 1 and having the relative parameters as noted above with respect to Fig. 4, the operating characteristics-are illustrated in Figs. 6 and '7. Fig. 6 illustrates the relationship for a single stage, activated by secondary electrons, between the electron multiplication or gain and the voltage, both the abscissae and ordinates being logarithmic. From this figure it will be seen that this relationship is linear over a wide range of voltages, which of source is highly desirable. and advantageous inasmuchras it enables satisfactory utilization :of the electron multiplier under a variety of conditions.

In Fig. 7, the output current of the electron multiplier is indi-cated with respect to the energization of the primary cathode, i. e., intensity of the light beam focussed upon the primary cathode indicated by the primary current therefrom, both the a-bscissae and ordinates being logarithmic. As clearly indicated :bythe family of l'characteristics in Fig. 7, each characteristic having a substantially 45 degree slope,.this relationship is linear over a wide range of interstage voltages, which also is highly desirable "and advantageous inasmuch as it assures uniformV op-f eration and amplification for a range of light intensities throughout a wide voltagerrange.

The departure from linearity indicated by the porti-on P in the 100-volt'per stage characteristic is attributable to space charge effects.

In modifications of the embodiment of Athis invention,Y illustrated diagrammaticallyand to scale in Figs. l to 4, the electrodes may beof the forms illustrated in Figs. 8, 9 and 10. In the modifications shown in these figures, the secondary cathodes differ from those in the specic embodimentv shown in Figs. 1 to 4eprincipally inthe` form of the emissive surfaces.V In other 75.

respects, the secondary cathodes may be substantially identical with those vshown in Figs. 1 to 4.

In the modification illustrated in Fig. 8, the emissive surface includes a curved portion B2b and a generally plane portion 32e, the radius of the curved portion being approximately 6 vunits and the dimension a'of the .plane portion being substantially 4.5 units. 'I'he other .parameters of the electrode structure may be substantially the same as those indicated hereinabove with respect to Fig. 4.

` In the modification illustrated in Fig; 9, the concave emissive surfaces 32 of the secondary cathodes are substantially continuously curved, the relative dimensions thereof and the space relation of the various electrodes being substantially the same as those indicated heretofore with reference to Fig. 4.

As shown in Fig. l9, auxiliary electrodes 5|, for example flat metallic plates orv strips, may be provided between adjacent ends of the electrodes for assisting in the formation of fields of the requisite and optimum directionl adjacent the emissive surfaces of the cathodes so that acceleration and convergence of electron streams are augmented and flow of electrons between successive` electrodes in the same row is prevented. The auxiliary electrodes 5I may be maintained at a positive potential, preferably somewhat higher thanthat of the preceding cathode in the same row, i. e., the next above cathode in Fig. 9, and also higher than the potential of the opposite cathode. It may be positive with respect to the succeeding electrode or equipotential and integral with it. l

In the modification illustrated in Fig. 10, the opposed surfaces 322 of the secondary cathodes are continuously curved and are inclined toward the medial plane passing through the line A'-A. The surface and spacing parameters may be substantially the same, except for the distances m1 and n1 and theangle 01, as given in connection with Fig. 4. The distances m1 and n1 may be 1.03 and 4.52 units, respectively, a typical unit being 0.0416 inch. The angle ,01, may be 71.8 degrees.

In Figs. 8, 9 and 10, the surfaces are drawn and spaced to scale and thereby indicate specific relationships of parameters whereby the desired field and convergence effects, among others, in accordance with the invention may be obtained.

In the embodiment of this/invention illustrated in Figs. 11 to 14, the enclosing vessel |20 is provided near one end thereof with a plurality7 of seals 52. The electrodes'are fabricated in aunitary structure supported from the stem |2| by a pair of semi-circular bands or collars4 53 clamped about the stem and having rigid posts or uprights 54 arising therefrom. The unitary electrode assembly includes an insulating spacer 55, such as a `mica disc, supported by the posts or uprights 54 and securely aflixed thereto, as by eyelets 56, and a pair of parallel insulating uprights 5l, for example .mica strips, having projections or tongues 58 extending through and fitted in slots in the disc 55.

Supported by and between the insulating uprights 51 are a primary cathode |25, an anode or collector electrode |26 and a' plurality of secondary cathodes |211 to |27B inclusive, the cathodes being mounted in two parallel rows and in staggered relation. The several secondary cathodes |212 to |2`|8 are identical in form and are arranged so that they have glide plane symmetry, have symmetry with respect to a longi- V:ijski 'current obtainable with given structudinal plane parallel to the insulating uprights 51 and are non-symmetrical with respect to any plane normal to the longitudinal plane and the medial plane,as described more fully in coiiec- Y tion'w'ith Fig. 1.

The secondary cathode |211 is substantially identical with the other cathcdesr except that it is somewhat shorter, the decrease in length being due to the lesser extension of the upper end. f

Each of the secondary cathodes, as*l "shown clearly inFig. 14,l may be formed of afstrip of metal, for example silver, and has a continuously The arms 59 extend through apertures-in the uprights 51 and maybe locked to the latter by integral bent-over'tabsl extending through suitable slots in the uprights. Electrical connection to the secondary cathodes may be established through leadingin conductors |35 each secured at one end to a corresponding one of the arms 59, extending through a suitable Aaperture in the disc 55 and sealed adjacent the other end in one of the seals 52. 1

The primary cathode |25 may be substantially identical with the secondary cathodes |212l to |21s inclusive, and supported in the same manneras the secondary cathodes. The concave surface thereof is photoelectrically active. For example, it may be treated to have thereon a coating or matrix including silver, caesium oxide Yand some free caesium.

As Will be noted clearly in Fig. 12, the concave portion |32 of each of the secondary cathodes |212 to |218 inclusive extends between'the corresponding emissive surface andA the next adjacent and-preceding cathode-in the same row so that the production of a retarding field effect, by such next adjacent preceding cathode, upon the electrons emanating' frorn such corresponding surface is prevented.

The anode or collector electrode |26 comprises -a plane metallic plateV section supported by `a pair yof Vbent kwires 15: extending into fthe uprights 51 shown in Fig. 10, the cathodes may be' maintained at successively'V equally higher potentials, as indicated in' Fig.- 15,* wherein elements corresponding to those of Figi 5 are designated by the same identifying numeral-increased by |08. The electron trajectories are indicated-by the arrows in Figs.`15 and '16. In lView of the de'- tailed description of Fig. given hereinabove,` the connections -to the cathodes and anode in Fig. will be clear without further; discussion.'V

As pointed out heretofore,l high eiciencyk and fully satisfactory operating characteristics require that strong fields away from the emissivesurfaces and a high degree of convergence'of the electron streams between the electrodes obtain. In addition, it is desirable'in' some instances that the .tare be availatie aiidutiii'zed. f In accordance with a feature of this invention,

the attainment ef these and other desiderata is facilitated by the provisionof auxiliary-electrodes 63 'te '|533 inclusive; in"clu'ji)erative relation with the 'several cathodes for' producing such fields that the electrons are subjected to strong accelerating and directive or focussing forces.

illustrative form, thesev auxiliary accelerating and vfocussing electrodes may be linear, small dial-heter nietallicrods'or wires extending betu'fivtlie insulating uprights 51 and fitted in apertures therein. The auxiliary electrodes 631 'to-.638 inclusiva-are located in the medial piane between the 'ro'vv'sf cathodes andthe electrode 63 'is aiiagedadjacent the upper end of the secondary cathode |2115 shw'n clearly inl Fig. 12, each ofthe auxiliary electrodes 63 is'- opposite the yccicave surface of a corresponding one of the cthdes and-*each of the electrodes 631 to 637 invc11':lsi\'fe#isinalignment with and adjacent the upper edge of the secondary cathodes |212 to |218 .nl-usi'v'e, respectively. That is to say, for example, the accelerating or focussing electrode 631 is opposite the concave surface of the first secondary' cathode |211an d in alignment with and ad- 'jacent the upper edge of the` secondary cathode i212.- Y U Electrical connection to the auxiliary electrodes G3 Yii-iayf beZ made individually through leading-in conductors 64- extendingv-through the disc 55 and Sealedir'l' the W-Il f the VesselA |20 at 52.

Each of the 'auxiliary electrodes 63 thus operated will produce a strong iield component away from the opposite emissive surface. Thus, the v auxiliary electrode' 63 'will produce a strong field away from the concave' surface of the primary cathode |25 and each ofthe electrodes 631 to 638 will produce a strong' field away from the concave surface of the secondary cathode |21 having the same superscript. Consequently, all of the electrons emanating from these surfaces will be drawn away therefrom and accelerated toward the next succeeding electrode so that the formation of space charge is prevented and, in addition, thefseco'ndary electron current may be voltage saturated even at relatively low interstage voltages'.

Furthermore, the strong fields produced by these auxiliary electrodes result in a decrease in thev transit time of electrons' between successive electrodes and reduce the effect of initial velocity rof the secondary electrons so that uniform characteristics for a Wide range of potentials and frequencies may be attained.

Finally, it will be appreciated that the auxiliary electrodes 63l produce fields which exercise a focussing' elect upon the several electron streams and aid in the attainment of convergence thereof. Specifically, it may be noted that these electrodes cause a turning or bending of the electron streams, as indicated bythe arrowsin` Fig., 15, so that electrons emanating from the cathodes are caused to impinge upon a restricted area of the next succeeding electrode. f

This turning or bending action is dependent upon the potential of the several auxiliary Yelectrodes and various desirable effects maybe achieved by adjustment of thesepotentials. For example, the potentials may be made such that the electrons arrive at each secondary vcathode,With a grazing incidence whereby more secondaryelec.- trons are producedv than by electrons impinging at normalincidence.

Furthermore, the potentials of one or moreoi the auxiliary electrodes 63 may bemadesllch vas to cause a very large bending orturning of the electron trajectories, suflicient to cause some of the electrons emanating from one or more cathodes to miss or pass by the next succeeding l cathode. Thus, the gain of the electron multiplier may be varied and its output may be modulated.

The auxiliary electrodes 63, as previously noted, have a small area so that the current thereto i very small. ,Y

The anode or collector electrode |26 may be partially surrounded by a plurality of shields orl screens 65, 66 and 61. The shield or screen 6,5 comprises two plate members at right angles to each other and supported by a pair .of crosswires 68 extending between the. insulating. up,- rights 51 and fitted in apertures therein. The shields or screens 66 and 61 may be metallic plates supported by wires 69 and 10, respectively fitted in apertures in the insulating uprights 51.

The shield 65 may be operated at the same potential as the secondary cathode |21", the shield 66 may be operated at the same potential may be operated at the same potential as the anode or collector electrode |26. Together with the anode, the several shields produce such fields between the secondary cathode |218 and collector electrode |26 that secondary electrons emanating from the latter are highly converged and focussed upon the collector electrode or `anode |26 or aA restricted portion thereof., l

As illustrated in Figs. 1l and l2, .the insulating uprghts 51 Vmay be provided with apertures 1| adjacent the ends'of the cathodes and Vthe anode to reduce end effects. d

Reference is made of the applicationsSerial No. 176,566, filed November 26,v 1937, of'JohnR.

205,930, nled May 4, 1938, of JohnR. Pierce wherein related inventions are ,disclosed and claimed. y

Although specific embodiments of thisinvienr tion have been shown and described and's'pecific parameters and potentials given, it will ,be ,understcod that these embodiments and values'are but illustrative andv that various modifications may be made therein without departing from the scope and spirit of this invention as deilned in the appended claims.

What is claimed is:

l. An electron multiplier comprising a pair of rows of secondary electron emissive members having opposed longitudinally concave, surfaces of varying curvature and mounted in staggered relation, a primary cathode at one end vof said rows, and a collector electrode at 'the ,otheriend of said rows.

.40 as the auxiliary electrode 637 and the shield 61 tion between said primary cathode and said collector electrode, each of said secondary cathodes having a continuously ,curved portion of varying radius of curvature the concave surface of which is toward the next preceding and next succeeding electrodes.

4. An electron multiplier comprising a `primary cathode, a collector electrode, and a plurality of secondaryv cathodes mounted ink staggered relation between said primary cathode and said collector electrode, each of said secondary cathodes beinginclined toward the next, preceding electrode and having its ends spaced unequal distances from the medial plane extending between said secondary cathodes, and said secondary cathodes having opposed surfaces concave.

5. An electron multiplier comprising a primary cathode, a collector electrode spacedfrom said vprimary cathode, a iirst row of closely adjacent secondary cathodes, a second row of secondary cathodes opposite said rst row, the secondary cathodes in said second row being in staggered relation'with the secondary cathodes in said rst row Yand each having portions laterally opposite two secondary cathodes in said vfirst row, the secondary cathodes in said rows having their opposed) faces longitudinally concave, land each secondary cathode being inclined toward the other row of cathodes with the end thereof remote trom `said primary cathode spaced from the medial plane between said rows a, distance greater than the spacing between the other end thereof and said medial plane.

6. An electron multiplier comprising a primary cathode, a collector electrode spaced from said primary; cathode, a row of aligned secondary cathodes one surface of each of which is concave in the direction of alignment of said secondary cathodes, and a second row of secondary cathodes each having a concave surface of varying radius v,of curvature facing and inclined toward said firstfrowof secondary cathodes.

55 Pierce and William Shockley and Serial No.

n 7.-, An electron multiplier comprising a primary cathode, a collector electrodev spaced from said primary cathode, aplurality of successively arranged secondary cathodes between` said primary cathode and said ,collector electrode,` and linear rod auxiliaryelectrodes opposite and substantially uniformly spaced from ythe emissive sur- .facespf certain of said'secondary'cathodes 8. electron multipliercomprising a primary cathodeha .collector electrode spaced. from` said V` I JIV imary-n cathode, vapair of rows of secondary lcathodes. );)etwe'en said,V primary cathode and said collec tor*electrode, said secondary cathodes having opposedwemissive surfaces, and a` plurality 0f auxliary--elsiwdes .mounted in a common boundary extending between` saidtwo rows, each auxiliary electrode beingubetween two correspondinglfacing' electrodes in said rows. Y

yelectron)multiplier comprising aprimary cathode, a collector electrode spaced from said primary cathode, Sarplurality of successively arranged secondary cathodes between said primary cathode and said collector electrode, said secondary cathodes having opposed emissive surfaces, an accelerating electrode opposite said primary cathode, and a plurality of field electrodes each opposite a corresponding one of said emissive surfaces.

- 10. An electron multiplier comprising a pair of rows of secondary cathodes having opposed emissive surfaces, a primary cathode adjacent one end of said rows, a collector electrode adjacent the other end of said rows, and a plurality of small area field electrodes between said rows, each eld electrode being opposite and substantially parallel tov a corresponding one of said emissive surfaces.

11. An electron multiplier comprising a pair of rows of secondary cathodes having opposed dished emissive surfaces, a primary cathode adjacent one end of said rows, a collector electrode adjacent the other end of said rows, and a linear auxiliary electrode opposite each of said surfaces.

12. An electron multiplier comprising a pair of rows of electrodes having opposed electron emissive surfaces, and a plurality of rod auxiliary electrodes between said rows, each of said rod electrodes being opposite a corresponding one of said emissive surfaces and parallel thereto.

13. An electron multiplier comprising a pair of rows of secondary cathodes having opposed concave emissive surfaces, the cathodes in one row being in staggered relation with those in the other, and a plurality of auxiliary electrodes between said rows, each of said auxiliary electrodes being opposite a corresponding one of said cathodes and substantially parallel thereto and adjacent the nearest edge of the next succeeding cathode.

14. An electron multiplier in accordance with claim 13 wherein said surfaces are uniformly spaced on opposite sides of the medial plane between said rows and said auxiliary electrodes are mounted substantially in said plane.

l5. An electron multiplier comprising a plu'- rality of secondary cathodes mounted in staggered relation in two parallel rows, opposed surfaces of said cathodes being curved toward one another, a primary cathode having a concave surface facing one end secondary cathode in one of said rows, a collector electrode opposite the other end secondary cathode in the other 0f said rows, a linear rod auxiliary electrode opposite said concave surface, and a plurality of parallel linear rod electrodes between said rows, each opposite a corresponding one of said secondary cathodes.

GORDON K. TEAL. 

